Combined Active Noise Cancellation and Noise Compensation in Headphone

ABSTRACT

The disclosure relates to combined active noise cancellation and noise compensation in a headphone. An audio processing device includes a selector and a noise compensation unit. The selector can select one of a plurality of first transfer functions based on at least one feature of at least one of an external noise and a content audio signal representing a sound to be reproduced through the headphone. The noise compensation unit can compute a second audio signal by applying the selected first transfer function to a first audio signal, and derive gains for the noise compensation at least based on the second audio signal. The at least one feature can be used to distinguish at least two of the first transfer functions. Each of the first transfer functions can transform the first audio signal to the second audio signal which is assumed as representing a version of the sound represented by the first audio signal, which arrives at an eardrum of a listener wearing the headphone. The first audio signal is one of a noise signal representing the external noise and the content audio signal.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.201410521327.3 filed on 30 Sep. 2014 and U.S. Provisional PatentApplication No. 62/074,881 filed on 4 Nov. 2014, both herebyincorporated in their entirety by reference.

TECHNICAL FIELD

The example embodiments disclosed herein relates generally to jointactive noise cancellation and noise compensation in headphone. Morespecifically, the example embodiments relate to headphones with audioenhancement in combined active noise cancellation and noisecompensation.

BACKGROUND

Techniques of active noise cancellation and noise compensation have beenproposed to improve headphone playback quality in the presence ofexternal interferences. Approaches of combining the noise compensationand the active noise cancellation have been proposed to benefit fromboth of them, for example, in WO2013144099A1, “Apparatus and Method forImproving the Perceived Quality of Sound Reproduction by CombiningActive Noise Cancellation and Perceptual Noise compensation,” thecontents of which are incorporated by reference herein in theirentirety.

FIG. 1 is a block diagram illustrating an example of an audio processingdevice 100 for performing combined active noise cancellation and noisecompensation in a headphone. As illustrated in FIG. 1, the audioprocessing device 100 includes a noise compensation unit 101, an activenoise cancellation unit 102 and a combiner 103.

The noise compensation unit 101 aims to enhance the headphone playbackquality by boosting an audio signal (also called content audio signal)to be played by the headphone. Specifically, the noise compensation unit101 is configured to obtain the spectral characteristics of a noisesignal captured from the external noise and selectively adjust theplayback level of the audio signal by deriving one or more gains inresponse. In determining the gains, in spectral regions in which thebackground noise is not deemed as distracting, the audio signal is leftlargely unmodified. However, in spectral regions in which the backgroundnoise level is high enough to negatively affect the perceived quality oraudibility of the audio signal, a level adjustment is made to the audiosignal to improve the audio quality for the listener.

The active noise cancellation unit 102 aims to enhance the headphoneplayback quality by reducing the noise level arriving at the listeners'eardrum. That is, it tries to generate a signal that has the inversephase with the residual noise, that is, external noise leaked throughthe headphone, and thus reduce the amount of noise arriving at theeardrum. In summary, it targets to enhance the audio quality byattenuating the level of the undesired external noise. It should benoted that the effectiveness of the noise cancellation technique islimited below (around) 1500 Hz. Cancellation of the higher frequencynoise is constrained by hardware limitations.

The combiner 103 combines the audio signal adjusted by the noisecompensation unit 101 and the signal generated by the active noisecancellation unit 102 and outputs a combined audio signal so as toreproduce it through a speaker 104 of the headphone. Alternatively, thecombiner 103 may be incorporated in the active noise cancellation unit102. In this situation, the active noise cancellation unit 102 may giveboost to the audio signal played by the headphone to further enhance thesignal to noise ratio.

SUMMARY

According to an example embodiment, there is provided an audioprocessing device for performing combined active noise cancellation andnoise compensation in a headphone. The audio processing device includesa selector and a noise compensation unit. The selector can select one ofa plurality of first transfer functions based on at least one feature ofat least one of an external noise and a content audio signalrepresenting a sound to be reproduced through the headphone. The noisecompensation unit can compute a second audio signal by applying theselected first transfer function to a first audio signal, and derivegains for the noise compensation at least based on the second audiosignal. The at least one feature can be used to distinguish at least twoof the first transfer functions. Each of the first transfer functionscan transform the first audio signal to the second audio signal which isassumed as representing a version of the sound represented by the firstaudio signal, which arrives at an eardrum of a listener wearing theheadphone. The first audio signal is one of a noise signal representingthe external noise and the content audio signal.

According to an example embodiment, there is provided a signalprocessing method of performing combined active noise cancellation andnoise compensation in a headphone. According to the method, one of aplurality of first transfer functions is selected based on at least onefeature of at least one of an external noise and a content audio signalrepresenting a sound to be reproduced through the headphone. A secondaudio signal is computed by applying the selected first transferfunction to a first audio signal. Gains for the noise compensation arederived at least based on the second audio signal. The at least onefeature can be used to distinguish at least two of the first transferfunctions. Each of the first transfer functions can transform the firstaudio signal to the second audio signal which is assumed as representinga version of the sound represented by the first audio signal, whicharrives at an eardrum of a listener wearing the headphone. The firstaudio signal is one of a noise signal representing the external noiseand the content audio signal.

According to an example embodiment, there is provided a headphone. Theheadphone includes one audio processing device as described in theabove.

According to an example embodiment, there is provided a headphone. Theheadphone includes a first audio processing device and a second audioprocessing device as described in the above. The first audio processingdevice is associated with one ear cup of the headphone, and the secondaudio processing device is associated with another ear cup of theheadphone.

Further features and advantages of the example embodiments, as well asthe structure and operation of various embodiments, are described indetail below with reference to the accompanying drawings. It is notedthat an example embodiment are not limited to the specific embodimentsdescribed herein. Such embodiments are presented herein for illustrativepurposes only. Additional embodiments will be apparent to personsskilled in the relevant art(s) based on the teachings contained herein.

BRIEF DESCRIPTION OF DRAWINGS

The example embodiments are illustrated by way of example, and not byway of limitation, in the figures of the accompanying drawings and inwhich like reference numerals refer to similar elements and in which:

FIG. 1 is a block diagram illustrating an example of an audio processingdevice for performing combined active noise cancellation and noisecompensation in a headphone;

FIG. 2 is a block diagram illustrating an audio processing device forperforming combined active noise cancellation and noise compensation ina headphone according to an embodiment;

FIG. 3 is a flowchart illustrating signal processing method ofperforming combined active noise cancellation and noise compensation ina headphone according to an embodiment;

FIG. 4 is a block diagram illustrating an audio processing device forperforming combined active noise cancellation and noise compensation ina headphone according to an embodiment;

FIG. 5 is a flowchart illustrating signal processing method ofperforming combined active noise cancellation and noise compensation ina headphone according to an embodiment;

FIG. 6 is a schematic view illustrating non-limiting exampleconfigurations of a headphone with combined active noise cancellationand noise compensation according to an embodiment.

DETAILED DESCRIPTION

The example embodiments are below described by referring to thedrawings. It is to be noted that, for purpose of clarity,representations and descriptions about those components and processesknown by those skilled in the art but unrelated to the exampleembodiment are omitted in the drawings and the description.

As will be appreciated by one skilled in the art, aspects of the exampleembodiment may be embodied as a system, method or computer programproduct. Accordingly, aspects of the example embodiment may take theform of an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, microcode, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the example embodiment may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof.

A computer readable signal medium may be any computer readable mediumthat is not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wired line, optical fiber cable, RF, etc., or any suitable combinationof the foregoing.

Computer program code for carrying out operations for aspects of theexample embodiments may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages.

Aspects of the example embodiments are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments. Itwill be understood that each block of the flowchart illustrations and/orblock diagrams, and combinations of blocks in the flowchartillustrations and/or block diagrams, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, special purposecomputer, or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the flowchartand/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

Noise compensation algorithms aim to improve perceived quality oraudibility of content audio signals. In executing the noisecompensation, the perceived quality or audibility is evaluated based onestimated noise and sound reproduced from (also called represented by)the content audio signal arriving at eardrums of a listener wearing aheadphone. The external noise is usually represented by a noise signalcaptured from environment. Noise or sound arriving at the eardrum isusually represented by an audio signal which is assumed as beingcaptured therefrom at the position of the eardrum (called estimatednoise or audio signal respectively). In scenarios of combined activenoise cancellation and noise compensation, those skilled in the art willappreciate that a path for transferring the external noise to an eardrumof the listener can have difference responses in case of differentlevels of the external noise, different levels of the content audiosignal, or different directivities of the external noise. Those skilledin the art will also appreciate that a path for transforming a contentaudio signal to a sound arriving at an eardrum of the listener can havedifferent responses in the case of different levels of the externalnoise, or different levels of the content audio signal. This means thatthe paths exhibit dependencies on some features of the external noise orthe content audio signal. Consideration of these dependencies in thenoise compensation algorithms can be helpful to improve accuracy ofestimation on signals arriving at the eardrum, and thus, to improve theperceived quality or audibility.

FIG. 2 is a block diagram illustrating an audio processing device 200for performing combined active noise cancellation and noise compensationin a headphone according to an example embodiment.

As illustrated in FIG. 2, the audio processing device 200 includes anoise compensation unit 201, an active noise cancellation unit 202, acombiner 203, and a selector 206. The active noise cancellation unit 202and the combiner 203 have the same functions as the active noisecancellation unit 102 and the combiner 103 respectively, and will not bedescribed in detail herein.

The selector 206 is incorporated to deal with at least one ofcombinations of the dependencies and the paths.

The dependencies are caused mainly by two factors. One factor is thefeature of the external noise and the content audio signal which canaffect the processing of the active noise cancellation and the noisecompensation, and thus affect the sound arriving at the eardrum. That isto say, the active noise cancellation algorithm and/or the noisecompensation algorithm perform the processing in a non-linear mannerover different values of the feature. Examples of the feature includebut are not limited to signal level and signal power. It can beappreciated that any aspect of the external noise and the content audiosignal which can affect the processing in a non-linear manner canfunction as one of such features. Another factor is the substantialdifference between paths. For example, in case of a moving externalnoise source, the path is changing over time because the path at onetime can be different from the path at another time. A similar situationmay occur in case of a moving listener. Therefore, the directivity ofthe external noise relative to the eardrum of the listener can functionas one of such features.

It can be appreciated that at least two different values of such afeature can indicate a difference in response of a path respectivelyunder situations of these two different values of the feature, andtherefore, such a feature can be used to distinguish the transferfunctions of the path under situations of these two different values offeature.

Non-limiting examples of dependencies of paths on specific features areillustrated in the following table.

Dependency Feature Path 1 Signal level or power of noise Noise 2 Signallevel or power of noise Audio 3 Signal level or power of audio Noise 4Signal level or power of audio Audio 5 Directivity of noise Noise 6Signal level or power of noise and audio Noise 7 Signal level or powerof noise and audio Audio 8 Signal level or power of noise andDirectivity Noise of noise

One specific dependency may be implemented as an association betweentransfer functions of a path and values of one or more features on whichthe path has the dependency upon. The value range of a feature may bedivided into bins represented by discrete levels respectively, andfeature values falling within a bin can be represented by thecorresponding level. The ordering and specific listing/label of featuresare merely provided as a non-limiting example for illustration purposesof some of example embodiments.

The dependency may also be implemented by generating a combined transferfunction with the value of the feature as an argument. The combinedtransfer function can apply a transfer function associated with thevalue of the feature. In the latter case, the function of the selector206 is incorporated into the combined transfer function, and when thecombined transfer function is applied, the function of the selector 206works.

In the embodiment as illustrated in FIG. 2, as an example of dependency1, each of transfer functions 205 is configured to transform a noisesignal representing the external noise to an estimated noise signalwhich is assumed as representing the external noise arriving at aneardrum of a listener wearing the headphone. The selector 206 isconfigured to select a transfer function based on the level of the noisesignal from transfer functions 205. The noise compensation unit 201 isconfigured to compute the estimated noise signal by applying theselected transfer function to the noise signal, and derive gains for thenoise compensation at least based on the estimated noise signal.

As an example of dependency 2, each of transfer functions 205 isconfigured to transform a noise signal representing the external noiseto an estimated noise signal which is assumed as representing theexternal noise arriving at an eardrum of a listener wearing theheadphone. The selector 206 is configured to select a transfer functionbased on the level of a content audio signal representing a sound to bereproduced through the headphone from transfer functions 205. The noisecompensation unit 201 is configured to compute the estimated noisesignal by applying the selected transfer function to the noise signal,and derive gains for the noise compensation at least based on theestimated noise signal.

As an example of dependency 3, each of transfer functions 205 isconfigured to transform a content audio signal representing a sound tobe reproduced through the headphone to an estimated audio signal whichis assumed as representing the sound arriving at an eardrum of alistener wearing the headphone. The selector 206 is configured to selecta transfer function based on the level of a noise signal representingthe external noise from transfer functions 205. The noise compensationunit 201 is configured to compute an estimated audio signal by applyingthe selected transfer function to the content audio signal, and derivegains for the noise compensation at least based on the estimated audiosignal.

As an example of dependency 4, each of transfer functions 205 isconfigured to transform a content audio signal representing a sound tobe reproduced through the headphone to an estimated audio signal whichis assumed as representing the sound arriving at an eardrum of alistener wearing the headphone. The selector 206 is configured to selecta transfer function based on the level of the content audio signal fromtransfer functions 205. The noise compensation unit 201 is configured tocompute an estimated audio signal by applying the selected transferfunction to the content audio signal, and derive gains for the noisecompensation at least based on the estimated audio signal.

As an example of dependency 6, each of transfer functions 205 isconfigured to transform a noise signal representing the external noiseto an estimated noise signal which is assumed as representing theexternal noise arriving at an eardrum of a listener wearing theheadphone. The selector 206 is configured to select a transfer functionbased on the level of the noise signal and the level of a content audiosignal representing a sound to be reproduced through the headphone fromtransfer functions 205. The noise compensation unit 201 is configured tocompute the estimated noise signal by applying the selected transferfunction to the noise signal, and derive gains for the noisecompensation at least based on the estimated noise signal.

As an example of dependency 7, each of transfer functions 205 isconfigured to transform a content audio signal representing a sound tobe reproduced through the headphone to an estimated audio signal whichis assumed as representing the sound arriving at an eardrum of alistener wearing the headphone. The selector 206 is configured to selecta transfer function based on the level of a noise signal representingthe external noise and the level of the content audio signal fromtransfer functions 205. The noise compensation unit 201 is configured tocompute an estimated audio signal by applying the selected transferfunction to the content audio signal, and derive gains for the noisecompensation at least based on the estimated audio signal.

FIG. 3 is a flowchart illustrating signal processing method 300 ofperforming combined active noise cancellation and noise compensation ina headphone according to an example embodiment.

As illustrated in FIG. 3, the method 300 starts from step 301. At step303, one of a plurality of transfer functions is selected based on atleast one feature of an external noise, a content audio signalrepresenting a sound to be reproduced through the headphone, or both theexternal noise and the content audio signal. The at least one featurecan be used to distinguish at least two of the transfer functions. Eachof the transfer functions is configured to transform a noise signalrepresenting the external noise to an estimated noise signalrepresenting the external noise arriving at an eardrum of a listenerwearing the headphone, or to transform a content audio signalrepresenting a sound to be reproduced through the headphone to anestimated audio signal representing the sound arriving at the eardrum.

At step 305, the estimated signal is computed by applying the selectedtransfer function to the noise signal or the content audio signal.

At step 307, gains for the noise compensation are derived at least basedon the estimated signal. The method 300 ends at step 309.

FIG. 4 is a block diagram illustrating an audio processing device 400for performing combined active noise cancellation and noise compensationin a headphone according to an embodiment.

As illustrated in FIG. 4, the audio processing device 400 includes anoise compensation unit 401, an active noise cancellation unit 402, acombiner 403, a selector 406, a microphone 407 and a detector 408. Thenoise compensation unit 401, the active noise cancellation unit 402 andthe combiner 403 have the same functions as the noise compensation unit201, the active noise cancellation unit 202 and the combiner 203respectively, and will not be described in detail herein.

In the embodiment as illustrated in FIG. 4, as an example of dependency5, each of transfer functions 405 is configured to transform a noisesignal representing the external noise to an estimated noise signalwhich is assumed as representing the external noise arriving at aneardrum of a listener wearing the headphone. The selector 406 isconfigured to select a transfer function based on the directivity of theexternal noise relative to the ear cup facing the eardrum.

As an example of dependency 8, each of transfer functions 405 isconfigured to transform a noise signal representing the external noiseto an estimated noise signal which is assumed as representing theexternal noise arriving at an eardrum of a listener wearing theheadphone. The selector 406 is configured to select a transfer functionbased on the directivity of the external noise relative to the ear cupfacing the eardrum and the level of the noise signal.

The microphone 407 is configured to record the external noise. Thedetector 408 is configured to detect the directivity based on the outputof the microphone 407. To detect the directivity, various techniques fordetecting the direction of arrival (DOA) of a sound source may beemployed. DOA algorithms like Generalized Cross Correlation with PhaseTransform (GCC-PHAT), Steered Response Power-Phase Transform (SRP-PHAT),Multiple Signal Classification (MUSIC), or any other suitable DOAestimation algorithms may be used.

FIG. 5 is a flowchart illustrating signal processing method 500 ofperforming combined active noise cancellation and noise compensation ina headphone according to an example embodiment.

As illustrated in FIG. 5, the method 500 starts from step 501. At step502-1, the external noise is recorded through at least one microphone.At step 502-2, the directivity of the external noise relative to the earcup facing the eardrum is detected based on the output of themicrophone. At step 503, one of a plurality of transfer functions isselected based on the directivity of the external noise and/or the levelof the noise signal. Each of the transfer functions is configured totransform the noise signal to an estimated noise signal which is assumedas representing the external noise arriving at the eardrum. Steps 505and 507 have the same functions as steps 305 and 307 respectively, andwill not be described in detail herein. The method 500 ends at step 509.

In the embodiments described in connection with FIG. 2 and FIG. 4,dependencies are considered to compute the estimated noise signal or theestimated audio signal. In further modifications to these embodiments,dependencies may be considered to compute both the estimated noisesignal and the estimated audio signal. The selector is configured toselect a transfer function for transforming the noise signal to theestimated noise signal from the transfer functions based on at least onefeature relating to the external noise and/or the content audio signal,and to select another transfer function for transforming the contentaudio signal to the estimated audio signal from the transfer functionsbased on at least one feature relating to the external noise and/or thecontent audio signal. The noise compensation unit is configured tocompute the estimated noise signal by applying the selected transferfunction to the noise signal, and to compute the estimated audio signalby applying the other selected transfer function to the content audiosignal. The noise compensation unit is further configured to derive thegains based on the estimated noise signal and the estimated audiosignal.

In the example embodiments described in connection with FIG. 3 and FIG.5, dependencies are considered to compute the estimated noise signal orthe estimated audio signal. In further modifications to theseembodiments, dependencies may be considered to compute both theestimated noise signal and the estimated audio signal. The step ofselecting may, for example include selecting a transfer function fortransforming the noise signal to the estimated noise signal from thetransfer functions based on at least one feature relating to theexternal noise and/or the content audio signal, and selecting anothertransfer function for transforming the content audio signal to theestimated audio signal from the transfer functions based on at least onefeature relating to the external noise and/or the content audio signal.The step of computing may, for example include computing the estimatednoise signal by applying the selected transfer function to the noisesignal, and computing the estimated audio signal by applying the otherselected transfer function to the content audio signal. The step ofderiving may, for example include deriving the gains based on theestimated noise signal and the estimated audio signal.

In further modifications to the embodiments described in the above,there can be an enhanced mode where the function of selecting a transferfunction and the functions relevant to the selecting, such as detecting,deriving and computing as described in connection with the embodimentsare executed. The enhance mode can be entered in response to an enablingindication. For example, this enabling indication may be triggeredthrough a user operation on a mode switch, in order to enable theenhanced mode for combined active noise cancellation and noisecompensation. In another example, the enhanced mode can be the only modefor combined active noise cancellation and noise compensation bydefault, and once the feature of active noise cancellation and noisecompensation is enabled, then the enhanced mode is enabled. The enablingindication may be implemented as a signal to receive, or a state orcondition to check or detect.

FIG. 6 is a schematic view illustrating non-limiting exampleconfigurations of a headphone with combined active noise cancellationand noise compensation according to an example embodiment.

FIG. 6 illustrates a headphone in portion (A). The headphone includes aleft-side audio processing device 603 and a right-side audio processingdevice 601 according to the example embodiments described in the above.The audio processing device 601 is associated with a right-side ear cup602, and the left-side audio processing device 603 is associated withleft-side ear cup 604. Although the headphone is illustrated asreceiving audio signals via a cable, it is also possible to receiveaudio signals via wireless connections such as Bluetooth and WiFi.

The transfer functions may be measured in advance with respect to theheadphone of a specific configuration. The measured transfer functionscan be deployed into headphones of the same configuration. Theconfiguration comprises the position relation of a microphone forcapturing the noise signal for the purpose of noise compensationrelative to the corresponding eardrum or ear cup. It is preferred tokeep this position relation stable or substantially fixed frommeasurement to actual usage, so as to facilitate improving the accuracyof estimation.

FIG. 6 illustrates several non-limiting example arrangements of themicrophone described in portions (B), (C) and (D).

According to the arrangement illustrated in portion (B), a microphone605 is, for example an inline microphone and is arranged near the jointof three cables. It is easy to keep this position stable and consistentin actual usage and measurement.

According to the arrangement illustrated in portion (C), a microphone605 is for example, coupled, attached to or embedded in the beltconnecting the left-side/right-side ear cups 602 and 604. It is easy tokeep this position stable and consistent in actual usage andmeasurement.

According to the arrangement illustrated in portion (D), microphones 605and 606 are coupled, attached to or embedded in the left-side/right-sideear cups 604 and 602 respectively, and are associated with theleft-side/right-side audio processing devices 603 and 601 respectively.It is easy to keep this position stable and consistent in actual usageand measurement.

The transfer functions can be measured according to the followingscheme. It is assumed that the transfer functions simulate an audio pathor a noise path and are dependent on features. In the measurement, foreach combination of levels of the features, at least one response of thepath is measured, and then a transfer function can be derived based onthe response. Under the requirement of keeping the combinationunchanged, the response of the path may be measured under various signalconditions. For example, if the transfer functions simulate a noise pathand the features include the level of noise signal, the signal conditionfor measurement cannot change because the level of noise signal isfixed. However, if the transfer functions simulate a noise path and thefeature is the level of audio signal, for example, it is possible tochange the level of noise signal and measure the response under variousnoise signal conditions.

Alternatively, a transfer function for simulating the noise path mayinclude a first portion for simulating a path for transferring theexternal noise represented by the noise signal to the eardrum with theactive noise cancellation being disabled, and a second portion forsimulating a change caused by the active noise cancellation to the path.The first portion is measured under the condition of disabling theactive noise cancellation. The second portion may be measured bycomparing the measurement result under the condition of disabling theactive noise cancellation and the measurement result under the conditionof enabling the active noise cancellation.

Alternatively, a transfer function for simulating the audio path mayinclude a first portion for simulating a path for converting the contentaudio signal to the version of the sound represented by the contentaudio signal, which arrives at the eardrum, with the active noisecancellation being disabled, and a second portion for simulating achange caused by the active noise cancellation to the path. The firstportion is measured under the condition of disabling the active noisecancellation. The second portion may be measured by comparing themeasurement result under the condition of disabling the active noisecancellation and the measurement result under the condition of enablingthe active noise cancellation.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the exampleembodiments. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the example embodiments has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimited to the example embodiments in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the exampleembodiments. The embodiment was chosen and described in order to bestexplain the principles of the example embodiments and the practicalapplication, and to enable others of ordinary skill in the art tounderstand the example embodiments for various embodiments with variousmodifications as are suited to the particular use contemplated.

The following example embodiments (each referred to as an “EE”) aredescribed.

EE1. An audio processing device for performing combined active noisecancellation and noise compensation in a headphone, comprising:

a selector configured to select one of a plurality of first transferfunctions based on at least one feature of at least one of an externalnoise and a content audio signal representing a sound to be reproducedthrough the headphone; and

a noise compensation unit configured to

-   -   compute a second audio signal by applying the selected first        transfer function to a first audio signal; and    -   derive gains for the noise compensation at least based on the        second audio signal, and

wherein the at least one feature can be used to distinguish at least twoof the first transfer functions, each of the first transfer functions isconfigured to transform the first audio signal to the second audiosignal which is assumed as representing a version of the soundrepresented by the first audio signal, which arrives at an eardrum of alistener wearing the headphone, and the first audio signal is one of anoise signal representing the external noise and the content audiosignal.

EE2. The audio processing device according to EE 1, wherein the at leastone feature comprises at least one of the directivity of the externalnoise relative to the ear cup facing the eardrum in case that the firstaudio signal is the noise signal, the level of the noise signal and thelevel of the content audio signal, and

wherein in case that the at least one feature comprises the directivity,the audio processing device further comprises:

-   -   at least one microphone configured to record the external noise;        and    -   a detector configured to detect the directivity based on the        output of the microphone.

EE3. The audio processing device according to one of EEs 1 to 2, whereinthe first audio signal is the noise signal, and each of the firsttransfer functions includes a first portion for simulating a path fortransferring the external noise represented by the noise signal to theeardrum with the active noise cancellation being disabled, and a secondportion for simulating a change caused by the active noise cancellationto the path.

EE4. The audio processing device according to one of EEs 1 to 2, whereinthe first audio signal is the content audio signal, and each of thefirst transfer functions includes a first portion for simulating a pathfor converting the content audio signal to the version of the soundrepresented by the content audio signal, which arrives at the eardrum,with the active noise cancellation being disabled, and a second portionfor simulating a change caused by the active noise cancellation to thepath.

EE5. The audio processing device according to EE 1, wherein the selectoris further configured to select one of a plurality of second transferfunctions based on at least one feature of at least one of the externalnoise and the content audio signal,

wherein the noise compensation unit is further configured to

-   -   compute a fourth audio signal by applying the selected second        transfer function to a third audio signal,

wherein the deriving of the gains comprises deriving the gains based onthe second audio signal and the fourth audio signal, and

wherein the at least one feature for selecting the second transferfunction can be used to distinguish at least two of the second transferfunctions, each of the second transfer functions is configured totransform the third audio signal to the fourth audio signal which isassumed as representing a version of the sound represented by the thirdaudio signal, which arrives at the eardrum, wherein the third audiosignal is one of the noise signal and the content audio signal, and thethird audio signal is different from the first audio signal.

EE6. The audio processing device according to EE 5, wherein the at leastone feature for selecting the second transfer function comprises atleast one of the directivity of the external noise relative to the earcup facing the eardrum in case that the third audio signal is the noisesignal, the level of the noise signal and the level of the content audiosignal, and

wherein in case that the at least one feature for selecting the secondtransfer function comprises the directivity, the audio processing devicefurther comprises:

-   -   at least one microphone configured to record the external noise;        and    -   a detector configured to detect the directivity based on the        output of the microphone.

EE7. The audio processing device according to one of EEs 5 to 6, whereinthe first audio signal is the noise signal, and each of the firsttransfer functions includes a first portion for simulating a first pathfor transferring the external noise represented by the noise signal tothe eardrum with the active noise cancellation being disabled, and asecond portion for simulating a change caused by the active noisecancellation to the first path, and

wherein each of the second transfer functions includes a third portionfor simulating a second path for converting the content audio signal tothe version of the sound represented by the content audio signal, whicharrives at the eardrum, with the active noise cancellation beingdisabled, and a fourth portion for simulating a change caused by theactive noise cancellation to the second path.

EE8. The audio processing device according to one of EEs 1 to 7, whereinthe selector is further configured to execute the operation of selectingin response to an enabling indication, and the noise compensation unitis further configured to execute the operations of computing andderiving in response to an enabling indication.

EE9. A signal processing method of performing combined active noisecancellation and noise compensation in a headphone, comprising:

selecting one of a plurality of first transfer functions based on atleast one feature of at least one of an external noise and a contentaudio signal representing a sound to be reproduced through theheadphone;

computing a second audio signal by applying the selected first transferfunction to a first audio signal; and

deriving gains for the noise compensation at least based on the secondaudio signal, and

wherein the at least one feature can be used to distinguish at least twoof the first transfer functions, each of the first transfer functions isconfigured to transform the first audio signal to the second audiosignal which is assumed as representing a version of the soundrepresented by the first audio signal, which arrives at an eardrum of alistener wearing the headphone, and the first audio signal is one of anoise signal representing the external noise and the content audiosignal.

EE10. The signal processing method according to EE 9, wherein the atleast one feature comprises at least one of the directivity of theexternal noise relative to the ear cup facing the eardrum in case thatthe first audio signal is the noise signal, the level of the noisesignal and the level of the content audio signal, and

wherein in case that the at least one feature comprises the directivity,the method further comprises:

recording the external noise through at least one microphone; and

detecting the directivity based on the output of the microphone.

EE11. The signal processing method according to one of EEs 9 to 10,wherein the first audio signal is the noise signal, and each of thefirst transfer functions includes a first portion for simulating a pathfor transferring the external noise represented by the noise signal tothe eardrum with the active noise cancellation being disabled, and asecond portion for simulating a change caused by the active noisecancellation to the path.

EE12. The signal processing method according to one of EEs 9 to 10,wherein the first audio signal is the content audio signal, and each ofthe first transfer functions includes a first portion for simulating apath for converting the content audio signal to the version of the soundrepresented by the content audio signal, which arrives at the eardrum,with the active noise cancellation being disabled, and a second portionfor simulating a change caused by the active noise cancellation to thepath.

EE13. The signal processing method according to EE 9, furthercomprising:

selecting one of a plurality of second transfer functions based on atleast one feature of at least one of the external noise and the contentaudio signal; and

computing a fourth audio signal by applying the selected second transferfunction to a third audio signal,

wherein the deriving of the gains comprises deriving the gains based onthe second audio signal and the fourth audio signal, and

wherein the at least one feature for selecting the second transferfunction can be used to distinguish at least two of the second transferfunctions, each of the second transfer functions is configured totransform the third audio signal to the fourth audio signal which isassumed as representing a version of the sound represented by the thirdaudio signal, which arrives at the eardrum, wherein the third audiosignal is one of the noise signal and the content audio signal, and thethird audio signal is different from the first audio signal.

EE14. The signal processing method according to EE 13, wherein the atleast one feature for selecting the second transfer function comprisesat least one of the directivity of the external noise relative to theear cup facing the eardrum in case that the third audio signal is thenoise signal, the level of the noise signal and the level of the contentaudio signal, and

wherein in case that the at least one feature for selecting the secondtransfer function comprises the directivity, the method furthercomprises:

recording the external noise through at least one microphone; and

detecting the directivity based on the output of the microphone.

EE15. The signal processing method according to one of EEs 13 to 14,wherein the first audio signal is the noise signal, and each of thefirst transfer functions includes a first portion for simulating a firstpath for transferring the external noise represented by the noise signalto the eardrum with the active noise cancellation being disabled, and asecond portion for simulating a change caused by the active noisecancellation to the first path, and

wherein each of the second transfer functions includes a third portionfor simulating a second path for converting the content audio signal tothe version of the sound represented by the content audio signal, whicharrives at the eardrum, with the active noise cancellation beingdisabled, and a fourth portion for simulating a change caused by theactive noise cancellation to the second path.

EE16. The signal processing method according to one of EEs 9 to 15,wherein the steps of selecting, computing and deriving are executed inresponse to an enabling indication.

EE17. A headphone comprising:

a first audio processing device according to one of EEs 1-7, which isassociated with one ear cup of the headphone; and

a second audio processing device according to one of EEs 1-7, which isassociated with another ear cup of the headphone.

EE18. The headphone according to EE 17, further comprising:

a microphone configured to capture the noise signal, and adapted to bearranged at a fixed location relative to the ear cups.

1-18. (canceled)
 19. An audio processing device for performing combinedactive noise cancellation and noise compensation in a headphone,comprising: a selector configured to select one of a plurality of firsttransfer functions based on at least one feature of at least one of anexternal noise and a content audio signal representing a sound to bereproduced through the headphone; and a noise compensation unitconfigured to compute a second audio signal by applying the selectedfirst transfer function to a first audio signal; and derive gains forthe noise compensation at least based on the second audio signal, andwherein the at least one feature can be used to distinguish at least twoof the first transfer functions, each of the first transfer functions isconfigured to transform the first audio signal to the second audiosignal which is assumed as representing a version of the soundrepresented by the first audio signal, which arrives at an eardrum of alistener wearing the headphone, and the first audio signal is thecontent audio signal.
 20. The audio processing device according to claim19, wherein the at least one feature comprises at least one of the levelof the noise signal and the level of the content audio signal.
 21. Theaudio processing device according to claim 19, wherein each of the firsttransfer functions includes a first portion for simulating a path forconverting the content audio signal to the version of the soundrepresented by the content audio signal, which arrives at the eardrum,with the active noise cancellation being disabled, and a second portionfor simulating a change caused by the active noise cancellation to thepath.
 22. The audio processing device according to claim 19, wherein theselector is further configured to select one of a plurality of secondtransfer functions based on at least one feature of at least one of theexternal noise and the content audio signal, wherein the noisecompensation unit is further configured to compute a fourth audio signalby applying the selected second transfer function to a third audiosignal, wherein the deriving of the gains comprises deriving the gainsbased on the second audio signal and the fourth audio signal, andwherein the at least one feature for selecting the second transferfunction can be used to distinguish at least two of the second transferfunctions, each of the second transfer functions is configured totransform the third audio signal to the fourth audio signal which isassumed as representing a version of the sound represented by the thirdaudio signal, which arrives at the eardrum, wherein the third audiosignal is the noise signal.
 23. The audio processing device according toclaim 22, wherein the at least one feature for selecting the secondtransfer function comprises at least one of the directivity of theexternal noise relative to the ear cup facing the eardrum, the level ofthe noise signal and the level of the content audio signal, and whereinin case that the at least one feature for selecting the second transferfunction comprises the directivity, the audio processing device furthercomprises: at least one microphone configured to record the externalnoise; and a detector configured to detect the directivity based on theoutput of the microphone.
 24. The audio processing device according toclaim 19, wherein the selector is further configured to execute theoperation of selecting in response to an enabling indication, and thenoise compensation unit is further configured to execute the operationsof computing and deriving in response to an enabling indication.
 25. Asignal processing method of performing combined active noisecancellation and noise compensation in a headphone, comprising:selecting one of a plurality of first transfer functions based on atleast one feature of at least one of an external noise and a contentaudio signal representing a sound to be reproduced through theheadphone; computing a second audio signal by applying the selectedfirst transfer function to a first audio signal; and deriving gains forthe noise compensation at least based on the second audio signal, andwherein the at least one feature can be used to distinguish at least twoof the first transfer functions, each of the first transfer functions isconfigured to transform the first audio signal to the second audiosignal which is assumed as representing a version of the soundrepresented by the first audio signal, which arrives at an eardrum of alistener wearing the headphone, and the first audio signal is thecontent audio signal.
 26. The signal processing method according toclaim 25, wherein the at least one feature comprises at least one of thelevel of the noise signal and the level of the content audio signal. 27.The signal processing method according to claim 19, wherein each of thefirst transfer functions includes a first portion for simulating a pathfor converting the content audio signal to the version of the soundrepresented by the content audio signal, which arrives at the eardrum,with the active noise cancellation being disabled, and a second portionfor simulating a change caused by the active noise cancellation to thepath.
 28. The signal processing method according to claim 25, furthercomprising: selecting one of a plurality of second transfer functionsbased on at least one feature of at least one of the external noise andthe content audio signal; and computing a fourth audio signal byapplying the selected second transfer function to a third audio signal,wherein the deriving of the gains comprises deriving the gains based onthe second audio signal and the fourth audio signal, and wherein the atleast one feature for selecting the second transfer function can be usedto distinguish at least two of the second transfer functions, each ofthe second transfer functions is configured to transform the third audiosignal to the fourth audio signal which is assumed as representing aversion of the sound represented by the third audio signal, whicharrives at the eardrum, wherein the third audio signal is the noisesignal.
 29. The signal processing method according to claim 28, whereinthe at least one feature for selecting the second transfer functioncomprises at least one of the directivity of the external noise relativeto the ear cup facing the eardrum, the level of the noise signal and thelevel of the content audio signal, and wherein in case that the at leastone feature for selecting the second transfer function comprises thedirectivity, the method further comprises: recording the external noisethrough at least one microphone; and detecting the directivity based onthe output of the microphone.
 30. The signal processing method accordingto claim 19, wherein the steps of selecting, computing and deriving areexecuted in response to an enabling indication.
 31. The headphone ofclaim 19, further comprising: a first audio processing device associatedwith one ear cup of the headphone; and a second audio processing deviceassociated with another ear cup of the headphone.
 32. The headphoneaccording to claim 31, further comprising: a microphone configured tocapture the noise signal, and adapted to be arranged at a fixed locationrelative to the ear cups.